It is known that organic polymers containing at least one reactive silyl group in the molecule have properties such that they are crosslinked under siloxane bond formation resulting from hydrolysis and other reactions of the reactive silyl group due to moisture and the like, even at room temperature to give rubber-like cured products.
Among these reactive silyl group-containing polymers, those polymers which have a polyoxyalkylene type or polyisobutylene type main chain skeleton are disclosed in Patent Document 1, Patent Document 2 and the like and have already been produced industrially and are in wide use in such fields as sealants, adhesives and coatings.
For obtaining cured products from a curable composition comprising such reactive silyl group-containing organic polymers, a silanol condensation catalyst is used. Generally used as the silanol condensation catalyst are organotin type catalysts having a carbon-tin bond such as dibutyltin bis(acetylacetonate) and dibutyltin dilaurate. In recent years, however, the toxicity of organotin type compounds have been pointed out and development of non-organotin catalysts has been looked for.
Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6 and Patent Document 7 disclose carboxylic acid tin salts and other carboxylic acid metal salts as silanol condensation catalysts and further disclose that the addition of an amine compound as a promoter to these catalysts results in improved curability.
Further, from the viewpoint of reduction in environmental stress, substantially metal-free catalysts are desired and, Patent Document 8 discloses the combined use system of an amine compound and a carboxylic acid for giving a metal-free silanol condensation catalyst.
However, when the non-organotin type catalysts described in the patents mentioned above are used, the adhesiveness of the cured products obtained tends to be inferior as compared with the use of organotin type catalysts.
While it is known in the art that the use of an amine compound in combination with another silanol condensation catalyst results in improved curability, as mentioned above, there is disclosed almost no examples in which amine compounds are used singly as silanol condensation catalysts.
In addition to amine compounds other than the above-exemplified compounds described in the patents mentioned above, Patent Document 9, Patent Document 10 and Patent Document 11 disclose, as silanol condensation catalysts, guanidine and diphenylguanidine which are included in guanidine compounds.
However, guanidines are chemically unstable compounds, hence they are not suited for use as silanol condensation catalysts. When guanidine compounds containing a plurality of aryl groups as substituents, for example diphenylguanidine, are used as silanol condensation catalysts, their catalytic activity tends to be low, as pointed out in Patent Document 12 as well.
On the other hand, Patent Document 12 discloses a technology which comprises using aryl group-substituted biguanide compounds, which constitute a group among amine compounds, as silanol condensation catalysts. Further, Patent Document 13 mentions tetramethylguanidine as an exemplary silanol condensation catalyst for siloxane-modified polyoxyalkylenes having a specific terminal structure, together with catalysts known in the art.
However, when the aryl group-substituted biguanide compounds described in Patent Document 12 are used as silanol condensation catalysts, the curable compositions obtained sometimes fail to show a practical level of surface curability; further, the compositions tend to be poor in depth curability in the early stage of curing.
The characteristic “depth curability” becomes important when the curable composition is to be used as an adhesive composition for industrial use, for instance. The problem is that when a curable composition poor in depth curability is used as an adhesive and bonded articles are transported while the adhesive inside is not yet in a sufficiently cured condition, the adherends may be finally bonded together in a condition shifted in relation to each other or bonding failure may be caused; hence, it becomes necessary to spend a long period of time for setting of the adherends.
Thus, this leads to decreases in working efficiency and the necessity of space for holding adherends and is a problem to be avoided from the practical viewpoint.
Further, when those guanidine compounds having no aryl group substituents which are described in Patent Document 13, for example tetramethylguanidine, are used as silanol condensation catalysts, the resulting curable compositions sometimes fail to show practical levels of surface curability and, further, fail to provide sufficient levels of adhesiveness in some cases.
Thus, in the existing circumstances, no curable composition balanced with one another among all curing behavior characteristics (surface curability, depth curability, adhesiveness, etc.) and capable of being submitted to practical use is found among the non-organotin type curable compositions which comprise a reactive silyl group-containing organic polymer and in which an amine compound-based silanol condensation catalyst is used.    Patent Document 1: Japanese Kokai Publication S52-73998    Patent Document 2: Japanese Kokai Publication S63-6041    Patent Document 3: Japanese Kokai Publication H05-39428    Patent Document 4: Japanese Kokai Publication H09-12860    Patent Document 5: Japanese Kokai Publication 2000-313814    Patent Document 6: Japanese Kokai Publication 2000-345054    Patent Document 7: Japanese Kokai Publication 2003-206410    Patent Document 8: Japanese Kokai Publication H05-117519    Patent Document 9: Japanese Kokai Publication H05-295248    Patent Document 10: Japanese Kokai Publication H05-32877    Patent Document 11: Japanese Kokai Publication H08-41359    Patent Document 12: Japanese Kokai Publication 2005-248175    Patent Document 13: Japanese Kokai Publication H09-12709